The union representing the 1,000 nurses working at Lenox Hill Hospital has warned they’ll hit the picket line in 10 days unless the two sides reach a deal on a contract.

The New York Professional Nurses Union vowed it will strike on Nov. 9, and called in federal mediation, after talks failed to prompt an agreement with the Upper East Side facility, its lawyer, Henry Berger, said yesterday.

The two sides remain “far apart on both substance and money,” Berger said.